The invention concerns an arrangement for controlling a hydraulic rock drilling device, said arrangement including a rock drill equipped with at least one actuator, a feed motor for feeding the rock drill in the drilling direction and reversing, a hydraulic pressure pump and the hydraulic fluid channels connected to it for feeding hydraulic fluid to each actuator and to the feed motor, and a return channel leading to a hydraulic fluid tank for returning hydraulic fluid to the hydraulic fluid tank, and valves for directing hydraulic fluid flow to each actuator and to the feed motor.
A variety of rock drilling control methods have been used with the aim to improve drilling results as well as to prevent the equipment from breaking. In many cases, the intent is to optimize the drilling process in some way to satisfy both cost and production objectives. A quite common principle is to use low feed speed and percussion power during collaring and, when collaring is completed, switch over to full feed speed and percussion power. This change-over is accomplished by either directly shifting from collaring values to normal drilling values or through a suitable ramp between them.
In the known controlling methods for drilling, the relation of feed pressure and percussion mechanism pressure is regulated so that the pressure difference between them remains constant. There are also solutions where both the percussion mechanism pressure and the feed pressure are connected to follow the hydraulic fluid pressure of the rock drill rotation motor.
The known solutions have several disadvantages. When regulating is based on constant pressure difference between percussion and feed pressures, it does not work optimally over a wide drilling power range. Therefore, at the extremes of the operating range of drilling either underfeed or overfeed will occur. This is especially the case when difference between feed pressure and percussion mechanism pressure values is great. Correspondingly, a small difference in the pressure values easily causes the percussion pressure to drop below the minimum set value when feed pressure drops, for instance, due to soft material, and this leads to problems in drilling.
U.S. Pat. No. 4,074,771 presents a solution where feed is adjusted using a manual control lever. The publication discloses that the operation of the percussion mechanism is installed to follow feed motor pressure so that when feed motor pressure exceeds a set limit value the hydraulic pressure in the percussion mechanism will rise in accordance with feed pressure. The publication states that during normal drilling the extreme position of the control lever will provide feed and percussion at maximum power. In this situation, the hydraulic pressure of the rotation motor is also connected to follow feed pressure so that if feed pressure decreases, rotation power will also decrease. The solution presented in the publication is complex, and its operation in drilling is not optimal. When feed, percussion, and rotation are connected to be regulated simultaneously, problems will arise and, for instance, collaring is difficult.
The purpose of this invention is to provide an arrangement for controlling rock drilling equipment so that drilling with all its phases can be easily and effectively realized, and that is uncomplicated for the operator to manage. The arrangement according to the invention is characterized in that the arrangement includes a pressure ratio valve that is connected during drilling to control the pressure of the hydraulic fluid fed to at least one actuator according to the pressure of the hydraulic fluid fed to the feed motor so that at least when the pressure of the hydraulic fluid fed to the feed motor exceeds a preset value the pressure ratio valve will control the pressure of the hydraulic fluid flowing to the actuator in a way that a change in the feed pressure causes a pressure change in the pressure of the hydraulic fluid fed to the actuator, and that this change has a constant relation to the pressure change in the hydraulic fluid fed to the feed motor as determined by the pressure ratio valve.
The essential idea of the invention is that the relation of the pressures in the pressure channel to the percussion mechanism and/or other actuator, such as the shank stabilizer, and in the pressure channel to the feed mechanism is regulated using a pressure ratio valve that will maintain the relation of the pressures to the actuator and the feed mechanism constant in the normal drilling range. A preferred version of the invention has a separate pressure relief valve connected to the actuator""s pressure channel, which keeps the hydraulic pressure to the actuator at a preset minimum pressure value in a situation where a pressure ratio valve would adjust the actuator""s pressure, in relation to feed mechanism pressure, lower than the said minimum pressure value.
A benefit of an arrangement pursuant to the invention is that percussion and feed functions, or the functions of another actuator and feed, are in a more favourable relation to one another with low as well as high power. A further benefit is that when using a simple pressure ratio valve, based on the surface areas of the regulator, it is easy and fast to change over to the desired pressure relation as required by the characteristics of the equipment and the drilling conditions. The preferred version of the invention has the further benefit, when a minimum pressure valve is used, of offering the possibility to set, for instance, the percussion mechanism minimum pressure such that under suitable conditions the percussion mechanism will also operate even with very low power.